BUG #6412: psql & fe-connect truncate passwords

The following bug has been logged on the website:

Bug reference:      6412
Logged by:          Andy Grimm
Email address:      agrimm@gmail.com
PostgreSQL version: 9.1.2
Operating system:   Linux (Fedora)
Description:=20=20=20=20=20=20=20=20

When psql prompts for a password, it only reads the first 100 characters of
the password.  The limit in fe-connect.c (for when .pgpass is used) is
weirder, a seemingly arbitrary 320 bytes for all fields combined.  Other
(postgresql-jdbc, PyGreSQL, etc.) have no problem with a 512-byte password.=
=20
It would be nice to have these limits controlled by a constant, and for the
command to give an error or warning when a password is truncated.